News

Making stretchy, foldable electronic circuitry

There are many applications in which it would be useful for circuits to be able to flex, bend or fold. These range from medical device applications to portable electronic devices.

Frost & Sullivan has therefore taken interest in work done by an international team of researchers that has developed a simple approach that should allow the production of stretchy, foldable integrated circuits that operate at high performance levels. The research has been reported in the journal Science.

"These systems combine high quality electronic materials, such as aligned arrays of silicon nano-ribbons, with ultrathin and elastomeric substrates, in multilayer neutral mechanical plane designs and with 'wavy' structural layouts," said John Rogers, one of the authors of the report.

The work, he said, points the way to devices that require extreme mechanical deformations during installation or use, yet at the same time need electronic properties consistent with those of conventional semiconductor electronics systems. "We are opening an engineering design space for electronics and optoelectronics that goes well beyond what planar configurations on semiconductor wafers can offer," Rogers said.

To build the devices, the researchers first apply a thin 'sacrificial layer' of poly(methyl methacrylate) to a rigid substrate, then coat it with a thin layer of polyimide. Devices are built on the polyimide layer using fairly conventional methods.

Then, the sacrificial poly(methyl methacrylate) layer is etched away, freeing the devices on the polyimide substrate from the rigid backing. The devices are then applied to a prestrained rubbery sheet. Once the sheet is allowed to relax, the device layer buckles into wavy structures that are still fully functional, but have enough 'give' to be bent, folded or otherwise manipulated.

"We have gone way beyond just isolated material elements and individual devices to complete, fully integrated circuits in a manner that is applicable to systems with nearly arbitrary levels of complexity," said Rogers.

Circuits in the structures have fully reversible stretchability and compressibility without substantial strains in the circuit materials themselves. Rogers said that adding a thin encapsulating layer on top of the devices could improve them still further by helping to prevent delamination under high strain.

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